This gene encodes a kinase that phosphorylates sphingosine into sphingosine-1-phosphate, which is involved in cell differentiation, motility, and apoptosis. The encoded protein plays a role in maintaining cellular levels of sphingosine-1-phosphate. The gene product also enhances apoptosis in different cell types and suppresses cellular proliferation. In mast cells, the encoded protein is necessary for influx of calcium, protein kinase C activation, and cytokine production and degranulation. Alternative splicing results in multiple transcript variants. [provided by RefSeq].